Harmful effects to the eye from ultraviolet radiation (from about 100 nm to about 380-400 nm in wavelength) have long been known. Ultraviolet radiation has been linked to cornea, lens, and retinal damage, including macular degeneration, and is believed to be a major cause of yellow-cataracts.
More recently, the undesirable effects of high transmittance levels of blue light (wavelengths from about 380-400 nm to about 500-515 nm) have received attention. High levels of blue light radiation have also been linked to retinal damage, macular degeneration, retinitis pigmentosa, and night blindness. In addition, blue light tends to be scattered in the atmosphere, especially in haze, fog, rain, and snow, which in part can cause glare, and diminished visual acuity.
In addition to the problems encountered with ultraviolet and blue light radiation, which affects the entire population, there are reported in the literature various special requirements based on optical diseases or conditions, and on occupations or activities in which a person engages. For example, a person with cataracts, diabetic retinopathy, corneal dystrophy, albinism, or extreme photophobia will have special visual needs not possessed by the general population. Also, people who engage in certain outdoor sports or activities, e.g., skiers, baseball players, football players, pilots, and boaters are exposed to high levels of ultraviolet, blue, and visible light radiation which can affect visual acuity required in such activities. Drivers of motor vehicles also have specific needs in terms of reducing glare and enhancing visual acuity under bright, sunlit driving conditions and reducing headlight glare at night. For these specific needs, alteration of light transmittance over the spectrum of visible light including the blue-violet end of the visible spectrum to the red end of the spectrum may be necessary. Boundaries of the visible spectrum have been reported by various authors. Formerly, the visible spectrum was commonly accepted as extending from 400 to 700 nm. More recently, the limits of the visible spectrum have been stated to be 380-760 nm.
Tinted spectacle or eyeglass lenses ("sunglasses") are used to reduce the amount of light transmitted to the eyes. Some sunglass lenses have incorporated an ultraviolet (UV) blocker to reduce the amount of UV incident upon the eyes. More recently, some sunglass lenses screen out both ultraviolet and blue light radiation. Sunglasses can be helpful to reduce the amount of light incident upon the eyes, but have various limitations which may make them unsuitable for certain activities. The use of sunglasses in sports activities is undesirable, as the sunglass frames may limit the field of view, particularly in peripheral viewing. Additionally, as the lenses are worn at a distance from the eyes, high-intensity light from around the lenses may be incident upon the eye, creating contrast aberrations and other unfavorable visibility conditions. Although attempts have been made to limit the light introduced from around sunglass lenses, such attempts are cumbersome and again may limit field of view.
Contact lenses positioned directly on the cornea of the eye have been used for correction of refractive errors of the eye. Tinting of contact lenses has developed for cosmetically altering the appearance of the eye or simply to allow the lens to be more easily handled. Some attempts have been made to provide the contact lenses with UV inhibitors for protection of the eye. Contact lenses are generally of two types, soft and hard, wherein soft lenses extend to the sclera, while hard lenses are positioned only on the cornea. Tinting may be provided over the entire lens, or only on a portion of the lens, for example that portion coinciding with the iris of the eye in a soft contact lens, for cosmetically altering the color of the person's eye.
Hard contact lenses, both tinted and clear, are polymeric in nature and employ as the matrix polymer a relatively hydrophobic transparent polymer, which is usually either methyl methacrylate (MMA) or a copolymer thereof. A hard lens may have incorporated therein either a polymerized or a nonpolymerizable ultraviolet (UV) absorber. For example, the 2-hydroxybenzophenones are known as UV absorbers. Their incorporation into plastics is also known. These compounds may be polymerizable, e.g., the 4,4'-di(acryloxy beta-hydroxypropyl) ether of 2,2',4,4'-tetrahydroxybenzophenone or non-polymerizable 2,2',4,4'-tetrahydroxybenzophenone and 2,2'-dihydroxy-4,4'-dimethoxybenzophenone.
Soft contact lenses, also widely called "hydrogel" contact lenses, are also polymeric in nature and employ a hydrophilic polymer is such as poly(2-hydroxyethyl methyl methacrylate) (polyHEMA) or a copolymer of 2-hydroxyethyl methacrylate. Various types of colorants for hydrophilic contact lenses have been reported. For example, both reactive dyes and vat dyes have been used as colorants for soft contact lenses. Vat dyes tend to leak or bleed out and so have not found widespread use. Reactive dyes, on the other hand will bond to the surface of the lens and do not bleed. Other types of dyes mentioned for hydrophilic contact lenses are water insoluble dyes and polymer bound dyes. Water insoluble dyes have a disadvantage in that a desired degree of tinting of a contact lens may not be obtainable because of the thinness of a contact lens.
Although both hard and soft contact lenses containing colorants are known, very little attention has been paid to the use of mixtures or combinations of colorants in contact lenses to obtain desired modification of transmittance characteristics in the visible spectrum. Therefore, in contrast to special purpose sunglasses or spectacles which are known, there is a need for special purpose contact lenses which will absorb substantially all incident UV and blue light and which have spectral transmittance characteristics over the remainder of the visible spectrum (e.g., about 500 to about 760 nm) which are tailored to meet specific needs of different categories of users.